The present invention relates to a functional film such as a gas barrier film constituted with organic and inorganic layers formed on a support, and a manufacturing method of the functional film.
In various apparatuses including optical elements, display apparatuses such as liquid crystal displays and organic EL displays, various semiconductor apparatuses, and solar cells, a gas barrier film is used for sites or parts that need to exhibit moisture-proof properties. The gas barrier film is also used as a material for packing foods, electronic parts, or the like.
The gas barrier film generally has a constitution in which a plastic film such as a polyethylene terephthalate (PET) film is used as a support (substrate), and a film exhibiting gas barrier properties (hereinafter, also referred to as a “gas barrier film”) is formed on the support. As films used as the gas barrier film, for example, films formed of various inorganic compounds such as silicon nitride, silicon oxide, and aluminum oxide are known.
Regarding a constitution that enables such a gas barrier film to exhibit a higher degree of gas barrier properties, a gas barrier film which has an organic layer (organic compound layer) as a base layer (undercoat layer) formed of an organic compound on a surface of a support and an inorganic layer (inorganic compound layer) formed of an inorganic compound exhibiting gas barrier properties on the organic layer, is known. Hereinafter, the gas barrier film which has the organic layer as a base layer and the inorganic layer on the organic layer is also called an organic/inorganic laminate-type gas barrier film.
For example, JP 2002-264274 A discloses a gas barrier film (transparent gas barrier laminate film) having a transparent plastic film as a support, an organic layer which is obtained by curing a UV-curable resin or an electron beam-curable resin and has a three-dimensional network structure on a surface of the support, and an inorganic layer on the organic layer.
Moreover, JP 2009-172986 A discloses a gas barrier film (barrier film substrate) having on a support an organic layer which is formed by polymerizing a mixture containing a monomer having two predetermined acrylate structures and a monomer having three or more of the same acrylate structures, and an inorganic layer on the organic layer.
As described in JP 2002-264274 A and JP 2009-172986 A, in the organic/inorganic laminate-type gas barrier film, the surface on which the inorganic film is formed is planarized through the organic layer formed on the support, whereby a high degree of gas barrier properties is obtained.
Generally, an organic layer is formed by a coating method using a coating material. Accordingly, the organic layer exhibits a high degree of self-leveling properties during the formation thereof, and can easily form a smooth surface. Consequently, when the film has such an organic layer, irregularities of a surface of the support are covered such that the surface can be smooth and planar.
When an inorganic layer exhibiting gas barrier properties is formed on such a planar organic layer, it is possible to form the inorganic layer while maintaining smoothness of the organic layer. As a result, a uniform inorganic layer that is not cracked, broken, or peeled can be formed throughout the entire surface, and accordingly, excellent gas barrier properties can be obtained.
Meanwhile, as described in JP 2007-277631 A, JP 2003-13020 A and JP 2007-21871 A, a large amount of foreign substances adhere on a surface of a plastic film which is mainly used as a support in the gas barrier film. The foreign substances are mostly residual oligomers formed during formation of the support, airborne particles that have electrically-charged and adhered, and the like. Most of the foreign substances have a size of about several micrometers.
In order to form an organic layer having a flat surface and completely covering (embedding) the foreign substances having such a size, in most cases, it is necessary to form an organic layer having a sufficient thickness for the state of the surface of the support, for instance, taking the foreign substances adhered on the support surface into account. That is, in order to obtain an organic layer having a flat surface as well as covering the foreign substances of about several micrometers, it is necessary to form an organic layer having a thickness exceeding 10 μm.
However, the thicker the organic layer is, the more easily cracks and the like occur in the organic layer. Further, when the support is a thin substance, curls and the like thereof are caused by the increased thickness of the organic layer.
Moreover, when the thickness of the organic layer is increased, the gas barrier film loses flexibility, and the original purpose for which the film is used cannot be achieved. In addition, the cracks or curls caused as above also significantly deteriorate the flexibility.
In addition, in view of productivity or costs of raw materials, the increase in the thickness of the organic layer is disadvantageous.
When the surface of the support is washed before the organic layer is formed, the above problems can be reduced to a large extent. Moreover, considering the quality of the gas barrier film to be obtained, needless to say, it is preferred for the surface of the support to be clean.
Therefore, as described in JP 2007-277631 A, JP 2003-13020 A and JP 2007-21871 A, in conventional gas barrier films, the support surface is cleaned by an adhesive roller or the like before an intended film is formed on the surface so as to remove foreign substances on the support surface, and then a film for achieving an intended function is formed on the support surface.
In particular, in the organic/inorganic laminate-type gas barrier film having a high degree of gas barrier properties with a moisture vapor transmission rate of less than 1.0×10−3 [g/(m2·day)] as described in JP 2009-172986 A, it is considered as important for the support surface on which an organic layer is formed to be clean such that the organic layer secures a higher degree of surface smoothness. This point is indisputable from the fact that JP 2009-172986 A discloses that it is preferred to form the organic layer (film) in a clean room.
Accordingly, in the organic/inorganic laminate-type gas barrier film, before the organic layer is formed on the support surface, the support surface is cleaned by using an adhesive roller or the like to remove foreign substances on the support surface, and then the organic layer and the like are formed to thereby form the organic layer having a flat surface.